Flotation dewaxing



United States Patent 2,847,356 FLOTATION DEWAXING Willem Johan Pieters,Lucas Alders, and Johannis Doom,

Amsterdam, Netherlands, assignors to Shell Development Company,Emeryville, Calif., a corporation of Delaware No Drawing. ApplicationSeptember 15, 1953 Serial No. 380,357-

Claims priority, application Netherlands September 10, 1952 8 Claims.(Cl. 196-'19) This invention relates to a process for the separation ofsolid wax from wax-containing oil, and particularly relates to a processfor the separation of a mixture of solid wax and oil, e. g., :of aparafiin wax concentrate, by means of flotation.

It is well-known to dewax oil containing solid wax by cooling the oil toa temperature at or slightly below the desired pour point of the toilproduct and separating the thus produced solid wax particles from thecooled oilwax mixture by flotation with a gas which is passed throughsaid mixture. The rising gas bubbles form a foam or froth on the surfaceof the oil, and the wax particles are entrained therein. Thewax-containing foam is then separated from the essentially solidwax-free bulk of the oil by any known process, such as skimming. Amongthe many foam-producing gases which are .suitable in this method areair, nitrogen, methane, ethane, propane, and the like. The gas can beintroduced into the oil-wax mixture from an external source, or it maybe. formed in situ, as, for example, by lessening the external pressureon a mixture of the wax, oil and .a liquefied gas, such as propane.

Although the flotation dewaxing technique has been known for many yearsand is an effective method of producing an oil substantially free of waxat the temperature of separation, practically no commercial applicationhas been made of it, this primarily because a substantial amount of oilis entrained with the'foam, which results in an uneconomically low yieldof .dewaxed oil as well as an undesirably high contamination of the waxproduct with oil.

A principal object of the present invention is to provide an improvedand commercially practicable method for the flotation dewaxing of awax-containing oil. A more specific object of the present invention is.toimprove the dewaxed oil yield in a process of flotationdewaxing.Another object is to make possible the recovery of a wax productcontaining a relatively smaller proportion of oilin a dewaxing processutilizing the wax flotation technique. Other objects of the inventionwill become apparent hereinafter.

It has now been discovered thatthe applicationior use of a small (minor)amount of a surface-active agent, which is at least partially oil.soluble :to the oil-wax mixture, will make possiblexthe attainment of amuch higher oil yield and a wax product of a much lower oil content,when these surface-active agents are used in the flotation dewaxing ofoils.

The mechanism by which these advantages are.accomplished is not entirelyclear. -In recent years much has been learned about theinterrelationship of surface forces in multi-phase systems, but-thedetermination-of factors which change these forces is still ordinarilyan empirical matter. With respect to the gas-oil-waxsystem encounteredin flotation dewaxing, it is plausible that when .no surface-activeagent is present .the .solid wax particles attract each other .andthereby have a tendency-to clot,

"the enclosed oil.

2,847,356 Patented Aug. 12, 1958 ice 2 resulting in the enclosure of oilbetween the wax particles. When such particles are entrained by the gasbubbles,

aggregates are formed which move with difficulty, do

not easily disintegrate and therefore no longer release It is possiblethat, when surface-active agents are added to the oil wax mixture thesurfaceactive agent will adhere to the wax particles and causethem torepel each other, so that clotting takes place to a lesser extent or notat all, the wax laden bubbles move more easily through the oil, andthere is less tendency for. the oil to become enclosed in the wax.Another possible theory is that the surface-active agent will decreasethe tendency of the oil to wet the wax particles (that is, will increasethe three-phase contact angle between the wax-oil interface and theoil-gas interface, through the oil phase) so that the oil will drainfrom the wax particles more rapidly. It is, at any rate, certain thatthe explanation is not a simple one. For example, in U. S. Patents Nos.2,645,597, 2,645,598, 2,645,599 and 2,645,600, there is set forth anexperimentally proven explanation of processes of dewaxing wherein anaqueous solution of a surface-active agent is employed to promote theseparation of oil-wax mixtures. In accordance with the teaching of thesepatents one would expect, as it is indeed expressly stated therein, thatthe aqueous phase is essential to the promotion of a separation of waxfrom an oil-Wax mixture by flotation, and yet we have found that such isnot the case. The essence of the present invention is the discovery thatthe addition of at least partially oil-soluble surface-active agents, incertain concentrations, directly to an oil-wax mixture will accomplishthe desired results and purposes set :out hereinabove and we thereforedo not wish to be limited to anytheoretical explanation.

In practicing the present invention, it is generally necessary to addonly a small quantity of a surface-active agent to the oil-wax mixture.It has been found that good results are obtained when the concentrationof the surface-active agent is as low as 0.01% by weight of the.mixture. 'In some cases it can be as high as 1.0% by weight. It ispreferred to use at least 0.05% by weight. Particularly good results areobtained when less than 0.7% by weight is added.

The surface-active agent used can be any of the-conventional chemicalsdenoted by that name which are at least partially oil-soluble. Forexample, particularly good results were obtained by the addition ofolefin polymers, such as Paratone (polyisobutene) and ethene oxidepolymers, such as Triton X-45 (a mixture of alkyl aryl polyethoxyalcohols). Other examples of the broad class of operable surface-activeagents useful 'in the practice of the invent-ion include alkyl oralkyl-aryl compounds substituted by one or more polar groups, inparticular alkyl-aryl sulphonates and alkyl-aryl phosphates, such ascalcium petroleum sulphonates, and alkyl salicylates, such as calciumalkyl salicylate. Silicones,

such'as Dow Corning D. C. 4 Compound, and condensation products ofchlorinated hydrocarbons and naphthalenes, such as Paraflow, are alsoespecially useful. The

surface-active agents can be used singly or in mixtures and is heated toa slightly higher temperature at which some,

but not all, of the wax is melted, and the flotation process repeated atthis slightly higher temperature. The waxfree or nearly wax-free oilphase from the first stage is then cooled to a lower temperature and theflotation process repeated at this lower temperature. Similarly, morestages can be used. In such a multi-stage process the foam phase fromeach stage will be transferred to the stage of the next highertemperature and the oil phase from each stage will be transferred to thestage of the next lower temperature, thus increasing the sharpness ofseparation between the wax and the oil by means of a rectificationeffect. A surface-active agent can be applied advantageously in each ofthe stages. It will also be evident that the technique can be carriedout in either a batch or a continuous process.

If the oil-wax mixture is too viscous for rapid separation of the wax,diluents can and should be added to it. For best results the viscosityof the mixture at the flotation temperature should not be higher than 50centipoises and preferably no higher than 25 centipoises. Althoughnon-polar solvents will usually be selected, it is occasionally ofbenefit to employ a relatively polar solvent.

As hereinabove stated, the process of the present invention does notrequire the presence of a separate aqueous phase. This improvement ishighly advantageous and greatly enhances the commercial practicabilityof the flotation process because an oil product, containing no morewater than does the charge stock, is obtained directly from thefloatation step without the necessity of subsequent and additionalseparation and drying steps. However, some of the charge stocks forwhich the process is suitable can contain some dissolved or dispersedwater in small quantities. Water in solution at the separationtemperature is not harmful and it has been found that as long as anyseparate water phase present amounts to less than about 1.0% by weight,and preferably less than about 0.5% by weight, based on the weight ofthe original oil-wax mixture, the benefits of the invention are stillrealized.

A particularly efiective method of practicing the invention is to usethe same substance as both the flotation gas and the refrigerant to coola waxy oil and precipitate the wax therein. Thus, liquefied propane, forexample, is mixed with the waxy oil containing a surface-active agentand permitted to vaporize by a lessening of the external pressure on thesystem. The resulting formation of gaseous propane reduces thetemperature of the oil and precipitates wax, and the rising gas bubblesproduce a wax-bearing froth, which can then be separated to recover thewax and oil products. Instead of propane it is possible to use anysubstance which is capable of vaporizing at the desired dewaxingtemperature. A large number of substances meet this requirement becausethe external pressure on the system can be adjusted at will to effectthe vaporization of the substance over a broad range of temperatures.Other examples of particularly suitable substances for the purpose arecarbon dioxide, ethylene and propylene. It will be evident to thoseskilled in the art that many other substances are also suitable. Thisparticular application of the process may be varied extensively. Forexample, the surface-active agent can be mixed into the oil eitherbefore or after the vaporizing material has been introduced into theoil. Any of the common viscosity-reducing dewaxing solvents or diluents,either polar or nonpolar, can be present. The process can be carried outin either a single stage or in several stages and it can be either batchor continuous.

The wax concentrate obtained by means of the present invention can befurther treated by any of the conventional methods of pressing,sweating, or'deoiling withsolvents if a purer wax is desired.

The following examples are given for the purpose of further elucidatingthe invention and to show especially effective applications of it, butare not to be considered limitations on its scope:

Example I A gas oil containing 1.4% by weight of solid wax at 10 C. wasseparated at this temperature by the conventional flotation technique asfollows: The oil-wax mixture was placed in a vertical tube the bottom ofwhich contained a frittered glass filter. Nitrogen was blown through thefilter into the oil-wax mixture. A foam layer was produced on thesurface of the oil and was recovered by skimming. The remaining oilphase was essentially free of solid wax as evidenced by its pour pointof 12 C. The oil phase yield was 75% by weight of the original mixture;therefore the recovered foam amounted to 25% by weight of the originalmixture and contained an oil to wax ratio of Next, in accordance withthe present invention, exactly the same procedure was followed exceptthat 0.5% by weight of Paraflow (condensation product of chlorinatedparaffin wax and naphthalene) was added to the original oil-wax mixture.The oil yield was thereby raised from 75% (by the conventionaltechnique) to by weight by the use of a surface-active agent inaccordance with the present invention. The oil to wax ratio in therecovered foam phase was reduced from 16.9 to 9.7.

Example II The conventional procedure of Example I was again repeatedexcept that now 0.1% by weight of Paratone (polyisobutene) was added tothe original oil-wax mixture. The oil yield was thereby increased to86.3% by weight and the oil to wax ratio in the foam was reduced to 8.8.

Example III The conventional procedure of Example I was again repeatedexcept that now 0.2% by weight of a 50% by weight solution of calciumpetroleum sulphonate in mineral oil was added to the original oil-waxmixture. The oil yield was thereby increased to 84.6% by Weight and theoil to wax ratio in the foam was reduced to 10.

Example IV The conventional procedure of Example I was again repeatedexcept that now 0.2% by Weight of a 50% by weight solution of calcium C-alkyl salicylate in mineral oil was added to the original oil-waxmixture. The oil yield was thereby increased to 78.0% by weight and theoil to wax ratio in the foam was reduced to 14.7.

Example V The conventional procedure of Example I was again repeatedexcept that now 0.1% by weight of Triton X-45 (an alkyl aryl polyethoxyalcohol) was added to the original oil-wax mixture. The oil yield wasthereby increased to 80.3% by weight and the oil to wax ratio in thefoam was reduced to 13.0.

Example VI The conventional procedure of Example I was again repeatedexcept that the original oil-wax mixture was a distillate gas oil from adiiferent crude oil. The oil. yield was 70% by weight. The addition of0.1% by weight of D. C. 4 Silicone Compound was added to a quantity oforiginal oil-wax mixture and the procedure repeated. The oil yield wasthereby increased to 86% by weight.

The present invention is applicable to all wax-bearing oils. The chargestock can be a distillate stock or a residue. Mineral oils, brown coaltar oils, shale oils, vegetable and animal oils and syntheticallyproduced oils, any of Which may have been previously subjected to adeasphalting treatment or other treatment for the purpose of improvingtheir physical and/or their chemical nature, are illustrative of sourcesof oils which can be advantageously dewaxed by the method of the presentinvention. The invention is applicable and advantageous in themanufacture of any of the usual products derived from theabove-mentioned sources, including, for exam ple, lubricating oils andgreases, furnace and other heating oils (both industrial and domestic),internal combustion engine fuels such as diesel oils and jet fuels, waxycharge stocks for cracking processes, wax products for industrial,pharmaceutical and chemical intermediate use, and many others.

We claim as our invention:

1. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of a minor amount of an at least partiallyoilsoluble surface-active agent.

2. In a flotation process of dewaxing oils wherein a mixture of solidWax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of from about 0.01% to about 1.0% by weightof an at least partially oil-soluble condensation product of chlorinatedhydrocarbon and naphthalenes.

3. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of from about 0.01% to about 1.0% by weightof an olefin polymer.

4. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the 6 presence of from about 0.01% to about 1.0% byweight of an alkyl-aryl sulphonate.

5. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awaxbearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of about 0.1% by weight of polyisobutene.

6. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awaxbearing. gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of about 0.2% by weight of a 50% by weightsolution of calcium petroleum sulphonate in mineral oil.

7. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of a passing ofa gas through said mixture to a surface thereof in the presence of lessthan about 1% by Weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprisingeifecting said passing of gas throughsaid mixture in the presence of from about 0.05% to about 0.7% by weightof a silicone compound.

8. In a flotation process of dewaxing oils wherein a mixture of solidwax and oil is separated into an oil product containing a smallerproportion of wax than in said mixture and a wax product containing asmaller proportion of oil than in said mixture by means of passing of agas through said mixture to a surface thereof in the presence of lessthan about 1% by weight of a separate aqueous phase thereby producing awax-bearing gaseous froth and a remaining oil phase as the only liquidphase and separating said wax-bearing froth from said remaining oilphase, the improvement comprising effecting said passing of gas throughsaid mixture in the presence of from about 0.01% to about 1.0% 'byweight of an at least partially oil-soluble condensation product ofchlorinated parafiin wax and naphthalene.

References Cited in the file of this patent UNITED STATES PATENTS1,277,935 Hussey Sept. 3, 1918 2,229,659 Carr Ian. 28, 1941 2,314,994Lawson et al Mar. 30, 1943 2,645,598 Myers et a1 July 14, 1953 2,645,599Payne July 14, 1953 2,658,854 Myers et a1. Nov. 10, 1953 2,719,817 DoornOct. 4, 1955 FOREIGN PATENTS 244,564 Germany Mar. 11, 1912

1. IN A FLOTATION PROCESS OF DEWAXING OILS WHEREIN A MIXTURE OF SAID WAXAND OIL IS SEPARATED INTO AN OIL PRODUCT CONTAINING A SMALLER PROPORTIONOF WAX THAN IN SAID MIXTURE AND A WAX PRODUCT CONTAINING A SMALLERPROPORTION OF OIL THAN IN SAID MIXTURE TO A SURFACE THEREPASSING OF AGAS THROUGH SAID MIXTURE TO A SURFACE THEREOF IN THE PRESENCE OF LESSTHAN ABOUT 1% BY WEIGHT OF A SEPARATE AQUEOUS PHASE THEREBY PRODUCING AWAX-BEARING GASEOUS FORTH AND A REMAINING OIL PHASE AS THE ONLY LIQUIDPHASE AND SEPARATING SAID WAX-BEARING FROTH FROM SAID REMAINING OILPHASE, THE IMPROVEMENT COMPRISING EFFECTING SAID PASSING OF GAS THROUGHSAID MIXTURE IN THE PRESENCE OF A MINOR AMOUNT OF AN AT LEAST PARTIALLYOILSOLUBLE SURFACE-ACTIVE AGENT.